1. Field of the Invention
The present invention relates, in general, to refrigerators and, more particularly, to a refrigerator which is provided with a freezer compartment and a refrigerator compartment.
2. Description of the Related Art
Generally, a refrigerator is designed such that a cabinet thereof is partitioned into a freezer compartment and a refrigerator compartment by a partition wall. A freezer door and a storage door are hinged to the cabinet so as to open or to dose the freezer compartment and the refrigerator compartment, respectively. An evaporator and a fan are mounted to an inside surface of the freezer compartment to produce cool air and supply the cool air into the freezer compartment. The refrigerator compartment is provided on an inside surface with an evaporator and a fan to produce cool air and supply the cool air into the refrigerator compartment. Thus, cool air is independently supplied into the freezer compartment and the refrigerator compartment, respectively. Such a system is referred to as an independent cooling system.
FIG. 1 is a view showing a closed refrigeration circuit for conventional refrigerators. As shown in FIG. 1, the dosed refrigeration circuit of a conventional refrigerator includes a compressor 101, a condenser 102, a capillary tube 104, a refrigerator compartment evaporator 105 and a freezer compartment evaporator 107 which are connected to each other by refrigerant pipes to perform a refrigeration cycle. In this case, the capillary tube 104 serves as an expansion unit. The dosed refrigeration circuit of the conventional refrigerator also includes a first motor 103a driving a condenser fan 103, a second motor 106a driving a refrigerator compartment fan 106, and a third motor 108a driving a freezer compartment fan 108.
In the conventional refrigerator, the freezer compartment is used to store frozen food. A known optimum temperature range of the freezer compartment is from −18° C. to −20° C. Further, the refrigerator compartment is used to store non-frozen food for a lengthy period of time to maintain a freshness of the non-frozen food. A known optimum temperature range of the refrigerator compartment is from −1° C. to 6° C.
Thus, the optimum temperature range of the refrigerator compartment is different from the optimum temperature range of the freezer compartment, but, in the conventional refrigerator, a refrigerant evaporating temperature at the refrigerator compartment evaporator 105 is equal to a refrigerant evaporating temperature of the freezer compartment evaporator 107. Thus, a temperature of the refrigerator compartment may be excessively and undesirably low. When the temperature of the refrigerator compartment is excessively low as such, an operating time of the refrigerator compartment fan 106 is appropriately controlled to prevent the refrigerator compartment from being super cooled. Since a pressure of the refrigerant in the capillary tube 104 is reduced according to the refrigerant evaporating temperature demanded by the freezer compartment evaporator 107, the above-mentioned problem arises. That is, when an extent of a pressure reduction of the refrigerant is determined based on the refrigerant evaporating temperature demanded by the freezer compartment evaporator 107, the refrigerant in the refrigerator compartment evaporator 107 evaporates under an excessively low temperature, and the temperature of the refrigerator compartment may fall below the optimum temperature for the refrigerator compartment. In this case, frost is formed on surfaces of the refrigerator compartment evaporator 107, thus undesirably hindering the refrigerator compartment from maintaining a high percentage of humidity. Furthermore, an evaporating efficiency of the refrigerator compartment evaporator 107 becomes low, thus resulting in a low cooling efficiency of the refrigerator. Since the refrigerant must be compressed in the compressor 101 in consideration of the refrigerant evaporating temperature demanded for the freezer compartment evaporator 107, a load imposed on the compressor 101 is increased, so an energy efficiency ratio of the refrigerator is low.